Method for removing a propeller assembly from and for mounting the same in an opening in the bottom of a swimming vessel

ABSTRACT

The invention relates to a method and apparatus for installing a propeller assembly in an opening in the bottom of a swimming vessel and for removing the propeller assembly from the opening. The propeller assembly comprises an underwater section including the actual propeller and a top section inside the vessel, between which is fitted a flange element for tightly sealing the opening. The apparatus comprises a hoisting chamber, which is fitted in the opening in the bottom of a vessel, extends inside the vessel to above waterline and surrounds the top section of the propeller assembly. The apparatus further includes guide elements for guiding the propeller assembly during the course of lifting or lowering. In the method, the propeller assembly is lifted away by way of the top of the hoisting chamber after clampings of the propeller assembly to the hull of a vessel are unfastened and hoisting means are secured to the propeller assembly. Installation proceeds in a reversed order.

BACKGROUND OF THE INVENTION

The present invention relates to a method as set forth in the preambleof claim 1 for removing a propeller assembly from and for mounting thesame in an opening in the bottom of a swimming vessel as well as to anapparatus as set forth in the preamble of claim 4.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved andrelatively simple and reliable method and apparatus for removing andmounting a propeller assembly for maintenance, repairs or replacementwithout having to bring the vessel to dock. This is particularlyimportant in connection with various rig platforms used by off-shoreindustry, said rigs being often designed to remain stationary for longperiods of time, e.g. up to 20 years. In the prior art, the propellerassemblies have been installed and removed from outside the vessel bymeans of various hoisting mechanisms. In a normal case, thesenecessitate the use of a diver for securing the hoisting cables to thepropeller assembly. A drawback in such externally performed removal andinstallation of a propeller assembly is that such operations are highlydependent on weather conditions. In poor weather, a diver cannot be usedfor such operations for reasons of safety.

In order to achieve the above-described object of invention, a method ofthe invention is characterized by what is set forth in thecharacterizing clause of claim 1. On the other hand, an apparatus of theinvention is characterized by what is set forth in the characterizingclause of claim 4.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described with reference made to theaccompanying drawings, in which

FIGS. 1-3 depict one apparatus of the invention at various stages ofremoving a propeller assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-3 illustrate an apparatus for removing a propeller assembly 1from and for mounting the same in an opening 9 in a vessel bottom 8. Theillustrated propeller assembly 1 comprises an underwater section 2,including the actual propeller, as well as a top section 3 inside thevessel, between which is a flange element 4 for tight sealing of theopening 9. The propeller is coupled through the intermediary ofappropriate gear means to a gear shaft 5, which is in turn connected topower means 6, e.g. an electric motor or a diesel engine. In thedepicted embodiment, the gear shaft 5 is removable. The opening 9 isassociated with a hoisting chamber 7, extending upwards inside thevessel to above waterline and having its bottom portion provided with apassage 13 for the gear shaft 5. The hoisting chamber 7 is designed tobe watertight.

Furthermore, inside the hoisting chamber 7 are included guide elements,not shown, for holding the propeller assembly 1 in a correct positionduring lifting and lowering.

The following describes the operations for removing and lifting thepropeller assembly 1 from the opening 9. The description is but anexample of one preferred implementation and is by no means intended tolimit the scope of protection defined in the claims for the invention.

Firstly, the gear shaft 5 is disengaged from between the top section 3of the propeller assembly 1 and the power unit 6, at the same timeremoving pertinent electrical wires and hydraulic tubes and otherpossible pipes. Next, the passage 13 is sealed with a watertight flange11 (FIG. 2) and the top section 3 of the propeller assembly 1 is coveredwith a watertight protective casing 10. The next step is to unfasten theclamping elements which secure the propeller assembly to the hull of avessel and to fasten hoisting cables 12 to the propeller assembly 1 andto let the water in the hoisting chamber 7. Finally, the propellerassembly 1 is lifted by way of the top of the hoisting chamber 7 andcarried away for necessary procedures. Installation of the propellerassembly 1 into the opening 9 proceeds in a reversed order. The removalof water remaining in the hoisting chamber 7 during the course ofinstallation can be effected by means of conventional pump equipment.

The apparatus can be subjected to a number of modifications withoutdeparting from the scope of protection defined in the claims for theinvention. For example, the top section 3 of the propeller assembly 1could be originally designed to be totally resistant to pressure water,whereby the use of a separate protective casing 10 is not necessary.

What is claimed is:
 1. A method for removing a propeller assembly,fastened to the hull of a swimming vessel, from an opening in the bottomof said vessel, said propeller assembly comprising an underwatersection, including a propeller, and a top section inside said vesselcoupled to power means for driving said propeller, said opening providedwith a watertight hoisting chamber with an open top extending above thewaterline inside said vessel and surrounding said top section of saidpropeller assembly, said underwater and top sections having therebetweena flange element for tightly sealing said opening, said power meansbeing located outside said hoisting chamber and coupled to saidpropeller assembly by means of a removable gear shaft, said gear shaftbeing adapted to extend through a passage in said hoisting chamber,including the steps of:releasing said propeller assembly from engagementwith said power means by removing said gear shaft; sealing said passagefor said gear shaft in a watertight fashion; unfastening said assemblyfrom the hull of said vessel; securing hoisting means to said topsection of said assembly; and lifting away said assembly through saidtop of said hoisting chamber.
 2. A method as defined in claim 1, whereinwater is let into said hoisting chamber prior to commencing, or during,the course of a lift.
 3. A method as defined in claim 2, furthercomprising mounting a protective casing over said top section of saidpropeller assembly prior to letting water into said hoisting chamber.